Method and apparatus for applying a viscous or paste material onto a substrate

ABSTRACT

An application device for applying viscous or paste fluid material to a surface therebeneath and having a fluid outlet aperture in its lower region and including a sealing gasket or foil for sealing the outlet aperture against the surface. The gasket or foil is formed from a sheet of flexible material with an uninterrupted or continuous, non-apertured outer part extending around the periphery of the outlet aperture and surrounding an inner aperture or apertured inner region of the gasket or foil.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for applying a viscous orpaste-like material through apertures in a stencil onto a substratebeneath the stencil and is particularly suitable for applying solderpaste onto a board for producing a printed circuit board or for applyingan adhesive or other bonding agent to a substrate via a stencil.

Control of the flow characteristics and composition of materials and thepressure thereof in the stencil printing onto substrates is veryimportant if good results are to be achieved.

Difficulty has been hitherto experienced in balancing or controlling thehigher pressure required for displacing solder paste from a reservoir todispensing pressure relative to the lower pressure required fordeposition at the actual stencil surface and it is with the resolutionof such difficulties with which our aspect of the present invention isconcerned.

With solder paste material and other materials which may containvolatile components it is important to confine the material within arelatively closed space to prevent evaporation and where the materialsare thioxotropic or contain such additives, it is important to minimiseany evaporation. It has now also been discovered desirable andadvantageous to maintain a movement of the viscous or paste-likematerial, especially immediately prior to application so as to maintainrelatively constant rheological characteristics of the soldering pasteand it is with this object with which a first aspect of the presentinvention is concerned.

Recent attempts have been made to provide improved apparatus forapplication of solder paste such as in WO/96/20088 of Ford Motor Co.Ltd. (PCT/GB95/03002) wherein a compression head cap provides acontained environment to direct and to aid the flow of pressurisedviscous material through openings (48) in the stencil. The compressionhead cap (8) includes two generally parallel wiper blades (78′,78)acting on the stencil with their end edges only that are in slidingcommunication with the stencil (46). Longitudinal diffusion plates (90)guide and equalise flow of the viscous material into the volume betweenthe two generally parallel and upwardly extending wiper blades (78′,178)acting on the stencil with their end edges only. In this apparatus theviscous material is forced through the interior chamber (66) of thecompression head (6) wherein it is diffused by a diffuser (90) with thematerial then flowing into the exit (68), and then on to the stencilsurface. EP-A-0504501 Zimmer and U.S. Pat. No. 4,023,486 also disclosesome of these features of Ford.

In WO 98/16387 Societe Novatec S. A. (PCT/EP97/05761) the apparatus ofthe Ford disclosure is described as not overcoming realised problems andpossessing various disadvantages. Specification WO 98/16387 of Novatecdiscloses a hollow receptacle (7) in which a piston (10) is displaceableto urge soldering paste (9) through apertures in a grill (17)functioning as a homogenising element upstream of two inclined wipermembers (15,16) and then between the upper members (15,16) and onto thestencil and through the apertures in the stencil. In this device thereare no means within the hollow receptacle (7) above the grill (17) forcreating a flow of paste material other than through the grill and,furthermore, a considerable amount of paste may remain in the spacedefined beneath the grill and partially encompassed by the wiperblades—which may lead to a reduction in quality of paste or othermaterial when the device is temporarily out of use. DEoffenlegungschrift 2250092 discloses a similar arrangement to Novatec.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is providedapparatus for use in a stencil printing machine which has a carriage forexecuting reciprocable movements or strokes, for applying a viscous orpaste fluid material to the surface of a stencil and through aperturestherein onto a substrate, said apparatus comprises a fluid materialapplicator device which is slideable along an upper surface of a stenciland has at least one aperture in the lowermost surface through which mayflow the fluid material to be deposited on the substrate below, at leastone fluid material reservoir or means for receiving such in fluidmaterial flow-communication with a flow passage in said applicatordevice, and means operable for displacing the fluid material during eachstroke of the stencil printing machine of an amount greater thannecessary to supply fluid material to the at least one outlet aperturefor deposition on the substrate via the stencil.

The greater amount of fluid material which is displaced in theapplicator device often requires a significantly greater pressure thandesirable for application of fluid material to the stencil, and it hasbeen found desirable for a pressure reduction means, such as a partitionwith one or more apertures or other flow restriction means, to beprovided prior to said at least one outlet and preferably between a mainflow passage of the applicator device or head and a passage leading tosuch outlet. A significant reduction of pressure is often required, suchas in the order of a ratio of 6 to 1, for example, in a reduction of say30 p.s.i. to 5 p.s.i.

In a second aspect according to the present invention there is providedapparatus for use in a stencil printing machine and for applying aviscous or paste-like material or other fluid material through aperturesin a stencil and onto a substrate beneath the stencil, comprising afluid material applicator device which is slideable along an uppersurface of a stencil in fluid retaining relationship therewith and has amain-flow passage in which fluid material may flow in alternatedirections or through which fluid material may flow in alternatedirections or in reciprocable manner or may flow intermittentlyinterruptably or continuously in the same direction and alsocommunicates with at least one aperture in the lowermost surface throughwhich may flow the fluid material to be deposited on the substrate, andat least one fluid material reservoir or means for receiving such influid material ducting flow-communication with said main-flow passage,and means for exerting pressure on said fluid material alternativelyfrom either end of said main flow passage preferably after each strokeof the printing machine, or means for exerting pressure intermittentlyor continuously in the same direction, with means preferably provided oravailable for accommodating the flow of fluid material resulting fromsaid pressure application which is additional to the flow of materialrequired for a deposition on the substrate.

Preferably two reservoirs will be provided one at either end of saidmain flow passage and preferably comprise two cartridges as pistoncylinder arrangements and with the pistons alternately displaceableduring each stroke of the stencil printing machine so as to drive fluidmaterial in opposite directions, even if only for two or threemillimeters, for example, to keep the level of the fluid moving duringprinting.

Preferably the lowermost surface of the applicator device is planar orsubstantially planar and the device is such as to enable the twopressure members of the printing machine, in use when the applicatordevice is located thereunder, to be urgeable against receiving means onthe upwardly facing side of the device, so that the planar lower surfaceis urgeable against the upper surface of the stencil on which it issliding and the pressure members alternate in application to be on thedownstream side of the device with respect to the direction ofdisplacement of the device and above the sealing edge of the at leastone lowermost aperture.

In one embodiment, an elongate slot as said at least one aperture isprovided for the passage of paste or other fluid although such may bemulti-apertured such as in the form of a grill or mesh or the like, andpreferably the sheet of material defining such will be integral andpreferably the sheet of material will provide an uninterrupted orcontinuous non-apertured region surrounding the apertured region.

Preferably the applicator device will have two reservoir meansconnectable and/or connected to be in communication with the oppositeends of the ducting means or main flow passage and displacing means suchas a piston may be provided for each reservoir means for enabling thefluid means in the free flow passage to be preferably alternatelydisplaceable from a first reservoir means into the main flow passage andfor some fluid already in the main flow passage to be displacedtherefrom into a second reservoir and vice versa.

The present invention may be provided as a removable/replaceableapparatus for a screen printing machine and the features of designmentioned herein enable optimum utilisation of the paste with minimumwaste. Preferably two reservoirs are provided, with each reservoir beingdetachably removable and replaceable with a fully charged like reservoirfor speed and simplicity of screen printing.

The apparatus of the present invention may be fitted/retrofitted toexisting screen printing machines whereby the previously used squeegeemembers are removed from the displaceable arms of the machine and thepresent apparatus located in position under and alternately held bymeans of the displacing arms as such are alternately reciprocatedupwardly prior to horizontal displacement by the carriage of theprinting machine. The displacement arms of the screen printing machineare normally alternately displaceable in upward and downward movement ofthe pressure members attached to the machine and shoulder or otherarm-receiving means are provided on the present apparatus to receive thepressure which facilitates fluid sealing of the applicator device insliding relationship on the stencil and also to enable the presentdevice to be horizontally driven in alternative directions.

The reservoir is preferably of light material such as plastics materialso as to possibly be disposable or rechargeable.

The apparatus of the present invention minimises the risk of viscousmaterials becoming stiff or otherwise unsuitable and also reduces amountof material which might be wasted and enables a rapid replacement of thereservoirs.

Also according to the present invention there is provided a pressurereducing and dispensing foil or foil members having in one embodimentthree walls or surfaces triangularly disposed or disposable andcomprising a lowermost, generally planar apertured wall having at leastone aperture therein for the throughflow and deposition of paste onto asubstrate, and two lateral walls extending from opposite elongate edgeregions of said lowermost wall and extending upwardly and converginglywith at least one said lateral wall having one or more pressure reducingapertures provided therethrough, and preferably a plurality of suchapertures spaced along each wall, and alignable with apertures in alower support or retaining member. Preferably the foil will have endwalls to close the ends of the defined passage.

Whilst the foil described above and illustrated in FIGS. 6A and 7 is onepiece, for ease of changing the lowermost apertured foil part or member,such foil may be provided in four parts, an upper apertured pressurereducing part, two lateral retaining parts with retaining edges forholding the main lower defined foil member defining the lowermost pasteexit aperture or apertures as will now be defined.

In a preferred embodiment, however, there is provided a pressurereducing foil comprising an apertured strip wherein the apertures whenlocated in an applicator device act to reduce the pressure in the fluidbefore it flows to the outlet defined by a separate lowermost flexiblefoil member which preferably has a continuous peripheral portiondefining the outlet aperture or apertures and in effect forms a fluidmedium printing gasket. Thus in a simple form of this preferred outletfoil or printing gasket, there is provided an elongate flexible foil ormetal sheet member having an elongate slot extending along its lengthand defined by the periphery or preferably detent means are provided forreleasably engaging with shoulders as thin retaining foils clamped onthe device. Preferably such retaining foils will have different foldlines so as to permit interchanging so as to provide for differentpositions of retention of the outlet foil. Alternatively, the lowerapertured foil member may be held laterally in channels formed in thebase of the applicator device instead of by lateral foil members.

Preferably resilient sealing means, such as a resilient ring, such as anO-ring will be provided in a groove to urge the lower foil memberdownwardly to seal against a stencil in use.

The present invention is intended to encompass such foils in flatunfolded form also.

Also according to the present invention a screen printing apparatuswhenever adapted or modified to incorporate the apparatus with pneumaticcontrol of the present invention.

It is also envisaged that an especially dedicated machine might beprovided rather than modification of existing or retrofitting ofexisting machine.

Also according to the present invention a method of applying a viscousor paste or like fluid material through a stencil to a substratecomprises displacing more fluid material than is necessary for theapplication of the fluid material to the substrate for each operativeapplication movement.

In a third aspect according to the present invention there is providedapparatus for use in a stencil printing machine and for applying aviscous or paste-like material or other fluid material through aperturesin a stencil and onto a substrate beneath the stencil, comprising afluid material applicator device which is slideable along andsupportable by an upper surface of a stencil in fluid sealingrelationship therewith and has a main flow passage which communicateswith at least one dispensing aperture in the lowermost surface throughwhich may flow the fluid material to be deposited on the substrate, andat least one fluid material reservoir or means for receiving such fluidmaterial in ducting flow communication with said main flow passage, andmeans for exerting pressure on said fluid material in said reservoir,and pressure reduction means for reducing the pressure of the fluidmaterial located between the dispensing aperture and said main flowpassage.

The lower-pressure ducting means is defined in part by a pressurereduction and carrier member which does not reduce in cross sectiontowards the sealing means or gasket but rather increases in transversecross section.

Said at least one dispensing aperture and the pressure reduction meansmay be provided as separate parts each of which is detachably mounted ona support and replaceable with an identical component, if one is worn ordamaged, or with a differently apertured component if a different fluidis to be applied. Also the pressure reduction means or part may bereplaceable as desired and may be modified as desired by selectingappropriate aperturing on the component and the manner of deposition ofthe fluid material from the device determined by selecting the requisitesize and/or shape and/or pattern or arrangement of the lowermostaperturing. This replaceable component may be formed by flexible sheetmaterial or foil and is indicated on the accompanying drawings as aninjector foil.

Preferably, the main housing or body of the applicator device accordingto the invention which defines the main flow passage and the reducedpressure flow passage interconnected by fluid material pressurereduction means is formed as one piece or integrally formed andpreferably formed by extrusion, for example, in aluminium. Theconstruction achieves considerable economy in manufacture and assemblyand ease of use. In this one piece or integral construction, thepressure reduction means is preferably formed as a slot or elongatepassage extending along preferably almost the whole of the length butterminating short of the ends.

This elongate pressure-reduction passage is advantageously formed byhaving the main body extruded with the main flow passage extendingtherealong, and preferably such that the lower sidewalls defining suchconverge (possibly somewhat in the manner of the section through thebottom of an inverted tear drop or water drop), and then machining inthe lower face of the housing a reduced-pressure flow passage or recess,terminating short of the ends, and machining or cutting into theconverging sidewalls defining the main passage to a sufficient extentand in a manner as desired to form an elongate slot or passage of awidth to achieve the required pressure reduction. The elongate slot maybe of constant cross-section or width or by varying the depth ofmachining may be of varying width, for example, may be narrowest nearthe inlet from the fluid reservoir or reservoirs and enlarge awaytherefrom to the middle and then converge again towards the other endand inlet of the other fluid reservoir when two such are provided. Thevarying of the width of the elongate slot is such as to distribute thefluid as evenly as possible along the slot and into the reduced-pressureflow passage

The outlet aperture defining member or printing gasket is preferably inthe form of a flexible metal foil with a continuous peripheral portionwhose inner edge acts as a fluid wiper and is preferably backed by aresilient member such as an O-ring. Preferably a spacing membersurrounds or substantially surrounds the gasket and is preferably of amaterial, such as PTFE, which facilitates sliding of the applicatordevice on a stencil and also is one determining factor as to how muchthe gasket foil is flexed against the O-ring in use. The provision ofthe spacing means or member around the gasket enables a gasket withdifferent length of aperture or apertures to be used and thus the deviceof the present invention can be used on substrates of different widths.

In a further aspect of the present invention there is provided a fluidapplicator device comprising a cross print-head or body means definingfluid ducting means and in communication with connection means, providedfor connection of a fluid reservoir means, and said ducting meansleading to an outlet passage in the lower surface of the device slidableon a substrate, characterised by the feature that the outlet passagecomprises an aperture or apertures through which fluid flows to bedeposited onto and through a stencil therebeneath, is defined by agasket or sealing means in the form of a thin sheet of material (such asa metal foil) having a continuous peripheral portion surrounding thepaste outlet aperture or apertures with an outer portion of said sealingmeans being secured to the body means or part thereof (preferablylocated in two parallel containing grooves or channels extendingparallel to a central elongate opening) and being supported on its uppersurface against yieldable means or resilient means (such as a rubberO-ring located in a groove) and which, peripheral portions inclinedownwardly preferably only slightly downwardly out of the horizontalplane or plane of the base of the body; and when not subject to counterpressure, the aperture defining edge(s) extends beneath the lowermostplane of the body means in which the lowermost surface(s) of the body orany spacing means lie by an amount such that when the applicator deviceis supported on a surface (such as on top of a stencil), the inner partof the peripheral portion and sealing edge of the gasket or sealingmeans are flexed/deflected upwardly against the counter pressure of theresilient means (preferably a rubber O-ring) so as to provide a slidingseal for preventing or minimising the escape of fluid.

Preferably spacing means or members (or a “shoe”) are provided locatedoutwardly of the aperture edges of the sealing means or gasket either atopposite ends and/or along opposite sides although preferably beingprovided located extending beneath and along and around all sides of theperipheral portion of the sealing means and leaving a central space intowhich the aperture—defining edge(s) of the deflected portions of thesealing means or gasket extend. Thus the aperture-defining edge(s) ofthe gasket or sealing means extend beneath the plane in which thelowermost surfaces of the spacing means lie by an amount such that, inuse, when supported on a stencil, the inner part of the peripheralportion of the sealing means is flexed upwardly against the resilientmeans so as to provide a sliding seal. The spacing means thus partiallyact to determine the pressure exerted by the gasket edges or sealingmeans.

Preferably the opposite ends of the gasket or sealing means will bepre-formed or pre-stressed so as to have a part-conical or hemisphericalor other curved surface or other shaped surface to improve the sealingeffect when flexed in use. Thus the resilient means e.g. an O-ring, actson the broad face of an inner part of the outer continuous peripheralportion and thus does not act on the outermost end edge where the gasketor sealing means is secured.

Thus also according to the present invention there is provided a sealingmeans or gasket for an applicator device for solder paste or other fluidfor use in stencil printing formed of an elongate, thin sheet offlexible material and comprising a continuous outer peripheral portiondefining an inner apertured region for the passage of fluid, withopposite end regions of the continuous peripheral portion beingpre-formed or shaped and pre-stressed to provide part conical endregions or an otherwise-curved or -shaped opposite end regions. This canbe achieved by forming a sheet blank as a development of the desiredresultant shape with straight parallel but inclined faces and of curvedopposite ends and which necessitates in the flat, a straight side withopposite end regions running into a side which is divided and ofinclined parts and then joining the parts to form the requisite partconical or other opposite end regions—when the elongate sides arepressed parallel with the outer edges lying in the same plane so as tothen become inclined.

Also according to the present invention there is provided a means foradapting a solder paste stencil printing machine having two reciprocablesqueegee blades detachably mountable in receivers in two vertically andhorizontally reciprocable carriers, comprising two elongate crossmembers securable by securing means in the receivers in the carriers andso as to extend parallel to each other, and a fluid applicator devicehaving at least one projection slidably engageable by one or both ofsaid cross members so as to enable said device to be reciprocablydisplaced upon operation of the machine. Preferably two projectionsextend from the device and are clamped between the cross members whichare vertically slidable relative thereto. Spring means may be providedto maintain pressure of each cross member on the applicator deviceirrespective of its vertical position.

Also according to the present invention, a method of applying a viscousor paste or like fluid material through a stencil onto a substratecomprises reducing the pressure of fluid material prior to it beingapplied to the stencil and substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a side elevation of a preferred embodiment of the apparatusaccording to the present invention viewed in/from the direction to whichor from which the apparatus is reciprocatably displaceable when mountedon a screen/stencil printing apparatus (not shown);

FIG. 1A is a schematic transverse cross section of the apparatus of FIG.1 illustrating the positioning of the apparatus of the inventionrelative to the vertically reciprocal pressure arms (only part shown)which exist on known screen printing machines (not shown) for applyinghitherto squeegees with one right-hand said pressure member beingdownwardly displaced in its operative pressure applying position and theother, elevated and prior to reversal of the positioning;

FIG. 2 is an enlarged schematic cross-sectional view of the apparatus ofFIG. 1 on its own and in through the region of one end;

FIG. 3 is a section illustrating the manner of securement with screwmeans of an applicator foil and foil retaining means with the mainapplicator device body also referred to herein as the main print headbody;

FIG. 4 is an enlarged fragmentary detail similar to FIG. 2;

FIG. 5 is a plan of an applicator foil device prior to folding of thelateral longitudinal sides and triangular ends and illustrating a singlerectangular aperture and surround which forms the lowermost surface ofthe device;

FIG. 6 is a transverse central section of the preferred applicator foilof FIG. 5;

FIG. 6A is a transverse central section of a modified applicator foil ofthe print head body of the apparatus of FIG. 1.

FIG. 7 is a similar view to FIG. 5 showing the applicator foil of FIG. 5in the left hand end and additionally showing other aperture-sizes andarrangements and shapings of applicator foils which might form thelowermost surface of the applicator device for depositing fluid materialfrom the apparatus;

FIG. 8 is a transverse section through the applicator device/ print headbody;

FIG. 9 is a side elevation of the device of FIG. 8;

FIG. 10 is a transverse section through the elevation of FIG. 11 of oneform of an applicator foil retaining member with threaded securingapertures in the apex and a row of through-flow passages either sideforming a means for reducing the pressure of the fluid material;

FIG. 11 is an elevation of the foil of FIG. 10;

FIG. 12 is an enlarged fragmentary section similar to FIG. 1Aillustrating alternative flanged edgings/reinforcements for thelowermost aperture;

FIG. 13 is a cross section through an alternative embodiment ofapplicator device and in particular of a main cross-head or print headbody with a three part injector foil;

FIG. 14 is a section through a modified foil retaining member on itsown;

FIG. 15 is a plan from below of the lower side of the foil retainingmember of FIG. 14 illustrating the two rows of paste ducting throughpassages (23′) surrounded by a rounded end continuous channel forreceiving a resilient endless band;

FIG. 16 is a plan of part of a preferred embodiment of applicator foildefining the lowermost aperture (elongate slot in this example) andwhich is held in position by two captive and angled lateral retainingfoils and which in use lies under the resilient band;

FIG. 17 is a plan of one of the two lateral retaining foils which holdthe applicator foil part of FIG. 16 in position and prior to bending ofthe lowermost edge along a score/partially etched line;

FIG. 18 is a view of a further embodiment of applicator device andcomprises a schematic plan from below of an applicator device onlyshowing a one-piece spacing member surrounding an applicator foil ormedia printing gasket similar to that of FIG. 16;

FIG. 19 is a perspective view from above, and partly an exploded view,of a preferred embodiment of applicator device according to theinvention;

FIG. 20 is a perspective view of the device of FIG. 19 having two supplycartridges attached and mounted on a known stencil printing machine bymeans of special mounting plates or adapters according to the invention;

FIG. 21 is an exploded perspective view from below of the device of FIG.19 showing an upper housing or body member with pressure-reduction andmounting means positioned in the ducting means and also showing a rigidmetal backing plate for a rectangular spacing member or shoe defining arectangular aperture;

FIG. 22 is a plan from below of the applicator device of FIG. 19;

FIG. 23 is a plan of a “keeper” or sealing member in the form of a clearplastics block with securing apertures and a closeable air bleedaperture;

FIG. 24 is a section on the line X—X of FIG. 22;

FIG. 25 is a plan of a sealing gasket or sealing means with a single,elongate rounded-end central aperture;

FIG. 26 is a plan of a gasket similar to that of FIG. 25 except there ismesh-like central part in which a plurality of apertures are provided asan alternative fluid exit control;

FIG. 27 is a plan from below of the pressure reducing and mountingmember showing a resilient O-ring in position but partially lifted outat the right-hand end;

FIG. 28 is a perspective view from above of the pressure reducing andmounting member on its own and with an additional pressure reducingplate for securement to the top and provided with smaller aperturessuitable for use with less viscous fluid;

FIG. 29 is a schematic illustration of what might be regarded as adevelopment of the eventual shape of a preferred form of sealing gasket;

FIG. 30 indicates the shape of such in the final form of use with thesides made parallel;

FIGS. 31 and 32 are plan views from below of one each of two a pairs of“blanking-off” plates to be used for shortening the effectiveapplication width of the applicator device when to be used on asubstrate of width narrower than the applicator device;

FIG. 33 is a plan from below of a blanking-off strip with parttransverse etching lines for snapping off two and blanking-off strips tosize;

FIG. 34 is a schematic illustration showing the location of ablanking-off strip;

FIG. 35 is an enlarged fragmentary section through an embodiment similarto FIG. 34;

FIG. 36 is a transverse schematic cross-section through a modificationof the embodiment of FIG. 21 wherein instead of a print head body andseparate mounting and pressure reduction means the two are integrallyformed as an extrusion; and

FIG. 37 is a preferred extrusion shaping with cavitied side walls forsavings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There is illustrated an apparatus 1 for use in a stencil printingmachine for applying paste media or other fluid material throughapertures in a flat stencil (not shown) on to a substrate or board (notshown) beneath the stencil and comprises an elongate fluid materialapplicator device or print head body 2 which is slideable along theupper surface of a flat stencil in fluid retaining relationshiptherewith and is formed of a main print-head body 3 (illustrated on itsown in FIGS. 8 and 9) which generally comprises two inclined limbs orportions 3′,3″ arranged in L-shaped mirror-like image disposition andwhich may be formed from an aluminium extrusion. A plurality of boltreceiving apertures 4 are provided at the apex of the body 3 throughwhich threaded bolts 5 may extend and be sealable therewith with thelower end of said bolts 5 being engageable in the threaded apertures 6′on the apex of the roof-like foil retaining member 6 so as to draw saidfoil retainer member 6 and any injector or applicator foil 7 thereoninto sealing engagement with the lower free ends of the disposed portion3′, 3″ so as to define a main flow passage 8 therewith.

The downwardly outwardly sloping outermost faces of the print head body3 also have threaded blind bores 9 therein to enable elongaterectangular stop plates 10 to be secured thereto by bolts 11 whichprovide shoulders 10′ for alternatively receiving the tips 12′,13″ ofthe pressure members 12,13 which are provided as adapter blades of thescreen printing machine and are locatable in place of known squeegeeblades on the printing machine and securable by threaded headed bolts insimilar manner as the squeegees. These pressure members 12,13 act bothto apply downward pressure on the body 3 and also to drive the wholeapparatus during each stroke of the printing machine. It is envisageddesirable (although not shown) for two cylindrical projections to beprovided extending upwardly from the central upper surface of body 3 andwhich are engageable in scalloped recesses or otherwise on the facingvertical surfaces of blades 12,13 so as to also centrally locate thepresent apparatus laterally and for a sliding contact to exist so thatthe blades 12,13 remain in contact at all times during operation in boththeir upper and lower positions.

At either end of the high pressure zone or main flow passage 8, anupwardly extending threaded duct 14 (opening as 14′ in an end block) isprovided in which there is screwable the lower end of a solder pastecartridge 15,16 having a pneumatically displaceable piston 17/18therein. A suitable cover (not shown) and pneumatic supply means (notshown) and control (neither shown) and provided so as to enablepressurisation on the space above the pistons 17/18 in each reservoirmeans or cartridge 15,16 and controlled to exert pressure thereon inalternate manner during the intermittent displacement stroke of thescreen printing apparatus to the present apparatus is attached to. Thuspressure is applied alternately to the reservoirs 15,16 causing a smallamount of paste to move alternately out of each reservoir and into thethrough passage 8 with a small amount alternately being displaced intothe other reservoir to which the pressure on its piston has beenremoved. During each stroke perhaps only a movement of approximatelyfive millimeters of paste in the passage 8 may take place. Withcontinued operation and alternate displacements, each of the reservoirs15,16 is gradually discharged via at least one opening 19 of the bottomof the applicator device which will be described hereinafter.

The foil retaining member 6 is an integral roof-like member also formedas an aluminium extension two elongate rectangular portions 20subtending an angle of 90° to each other with the angled apex beingformed or machined to be flat 20′ and normally horizontal. The lowerends of the portions 20 extend via a 90° corner into two lower endstrips or lower limbs 21 against which abut (via seals 22) the shapingfaces of the print seal body 3 with foil thereon sealingly abut. Thelowermost end faces machined to be horizontal although may be stepped soas to provide a shoulder 6′ of foil retaining member may be for purposeof intensifying the pressure around the lower opening 19.

As mentioned, apertures 4 are provided along the apex of body 3 forsecuring of the retaining member 6 against the end faces of the printhead body 3 and rubber seals 22 are provided therebetween to ensureappropriate sealing. In retaining member 6 and above the region of theseals 22, a row of apertures 23 are provided and form throughflowpassages for the passage of fluid paste from the main flow passage 8 tothe space defined between the limbs of the foil retaining member 6 andthe foil.

A combined lowermost aperture forming and pressure reducing member ormeans is formed by foil 7, as illustrated in FIGS. 5, 6, 6A and 7, whichcomprises an apertured and scored thin metal sheet which has portionswhich are folded over or slide along the foil retaining member 6 so asto overly such with the two rows of pressure reducing apertures 24aligning with the through passages 23 in the foil retaining member 3 andwith the single rectangular elongate rectangular aperture 19 andsurrounding continuous surface 19′ forming the lowermost surface of thedevice or other aperture arrangement such as, for example, alsoillustrated in FIG. 7 may be selected as desired. The pressure reducingapertures 24 are provided in rectangular side portions 25 and such arefoldable along score lines 26 and may be selected as regards size andnumber for the appropriate application (possibly to provide a pressurereduction of 6:1) and/or as may the shape and dimension and pattern etc.of the lowermost aperture(s) 19. Triangular end flaps 27 are foldablealong score lines 28 once the foil member 7 is located on retainingmember 6 to close the ends of the passage 8 and are clamped against theends of retaining member 6 via end plates 29 (with sealing means) whichare held in position via threaded tie rods 30 and bolts 31 actingagainst plates 29 at each end. A slight gap exists between the freelonger edges of portions 24 in the folded position.

It has been found highly desirable for the foil 7 in the region of theelongate rectangular aperture 19 have along the parallel longer sidesthereof two inclined extensions 7′ (shown in FIG. 6A) which are inclinedso as to converge together and to underly the lower inner inclinedsurfaces of the foil retaining member 6 preferably at the same angle asits lower surface and to abut thereagainst to provide for additionalstrengthening of the elongate rectangular aperture.

As mentioned end plates 20 with appropriate seals are provided atopposite ends of the foil retaining member 6 and print head body 3 withappropriate seals and are securable by threaded tie rods 30 with theknurled tightening ends 31. The tie rods pass through the apertures 29′in the end plates 29.

Thus in summary, with the injector foil 7 located over the foilretaining member 6, there is defined a generally triangular section lowpressure zone or passage 32 and the two components are sealingly clampedagainst the print head body 3 to form the high pressure zone or mainflow of passage 8 with the two zones being interconnected via theselected pressure reducing apertures 24 in the foil leading through thenormally longer apertures 23 in the foil retaining member 6 to the atleast one aperture 19 in the bottom of the foil 7 from whence paste mayflow at a suitable pressure to the stencil therebeneath.

Paste is supplied to the main flow passage 8 in body 3 from thereservoir cartridges 15,16 at either end under the alternate pressureaction of the upper pistons 17,18 thereof alternately driven by thepneumatic source (not shown) and in operation during a stroke of theprinting machine in one direction, pneumatic pressure is applied to thepiston of one reservoir cartridge 15/16 whilst the other cartridge 16/15is not pressurised. At the end of the stroke both reservoirs 15,16 arenot pressurised but on the next or return stroke, with paste beingapplied to another board placed beneath the stencil, the other reservoircartridge 16/15 is pressurised whilst the first cartridge 15/16 is notpressurised and the process continues accordingly.

The control means and pneumatic pressure for acting on the pistons aresuch that a large volume of paste exists in main flow passage 8 andwhich it is desired to keep in movement to maintain the characteristicsthereof and to condition such, and to achieve this a considerablygreater pressure (for example in the region of 30 p.s.i.) is requiredthan that necessary for the stencilling operation (such as 5 p.s.i.) andthus the apertures 24 are selected such as to achieve an appropriatereduction in pressure having regard to the nature of the paste materialetc. It is to be appreciated that during each “stroke” of the printingmachine (not shown) some paste material will flow from passage 8 intopassage 32 and from there hence to the stencil, and some material needsto flow from passage 8 to achieve sufficient movement (approximately 5mm in the main flow passage 8) and there is surplus flow into theunpressurised cartridge although other biased receiving means might beproposed.

In order to facilitate changing of the applicator foil, there is devisedand illustrated in FIGS. 13 to 17 an alternative embodiment ofapplicator foil and a modification of the apparatus of FIGS. 1 to 12 asillustrated wherein the main difference is that the applicator foil isformed in three pieces namely the main, lower aperture—definingapplicator one-piece foil member 33 with slot-like aperture 33′ which isto be held by two lateral retaining foils 34,35 having paste throughapertures 24′ and a retaining edge 36,37 bent along a fold line 38 toform a space beneath the lower face of the retaining part 6A havingthrough apertures 23′ leading to a central passage 39 and thence to thesubstrate via the elongate slot in foil member 33. Threaded apertures 6Bare provided for bolts 5 for clamping securement of the part 6A.

A continuous groove or channel 40 is provided in the lower surface ofpart 6A for partially receiving a resilient endless ring or band orO-ring 41 which extends out of the channel 40 to press against the uppersurface of foil member 33 around the slot thereof and act as a seal andalso to act as biasing means to cause the foil member 33 to be deflectedand/or flexed downwardly as shown in FIG. 13 and which is subject tocounter pressure when applied to the surface of a stencil to therebyincrease the sealing effect. The side edges 6C of part 6A are angled orprovide space for flexing of foil member 33 held captive by edges 36,37of foils 36,37.

It will be appreciated that foils 36,37 will inwardly and oppositelyfacing retaining edges 36,37, are claimed in position in the print headbody 2A closing off the main flow passage 8A therein whilst permittingflow via passages 23′. The foil member 33 can then be slid-in from oneend of the body 2A between edges 36,37 and the lower surface of part 6Aand the ring 41 to underlie the lower pressure zone 32A in part 6A.

The foil member 33 has a continuous outer peripheral portion surroundingthe slot 33′ to ensure sealing against escape of paste. Alternativeaperture arrangements are possible other than slot 33′ whilst keeping acontinuous periphery and the other apertured foil members may be readilyexchanged by sliding in from one end.

A spacing block 42 (only one shown in FIG. 13) is screwed by screws 43at opposite ends of the lower face of the print body 2A of a requiredthickness “t” to provide clearance beneath part 6A for the downwardflexing of foil 33 but under sufficient back pressure in use from thestencil (not shown) therebeneath for adequate sealing. These spacingblocks 42 across the ends of body 2A are preferably of a plasticsmaterial such as PTFE or polypropylene or like to facilitate slidingwith minimal wear. The blocks 41 also clamp the opposite ends of thefoils 34,35 and foil member 33 in position.

FIG. 18 is a schematic plan from below of an applicator device similarto that of FIGS. 13 to 16 but wherein instead of through passages 23,23′ in the sloping side walls of the retainer member 6, member 6 isprovided with a flat top surface, instead of the apex as shown in FIGS.1-16, and a plurality of through passages 44 (equivalent to passages23′) for the flow of fluid medium and has overlying such an elongatefoil (not shown) with smaller pressure reducing/flow restrictingapertures therein and aligned with apertures 44 is provided and clampedin position to overlie aperture 44.

A modified foil member 33M is provided and abuts a resilient O-ring in agroove (40) in similar manner to that of FIGS. 13-16 and is held inplace by retaining foils similar to foils 34, 35 at FIG. 17 but foilretaining detents 45 are provided for engagement with the regionsadjacent shoulders by fold lines 38 to retaining edges 36,37.

The amount retaining edges 36, 37 extend from member 6 is determined bysmaller edge flaps 46, separated by fold lines as indicated by brokenline 36′, 37′ in FIG. 17 and differently sized foils can be provided.

Instead of end spacing blocks 42 as illustrated in FIG. 13, the whole ofthe paste outlet aperture in the bottom of the applicator device of FIG.18 is surrounded by a spacing member or shoe 46 which in the example isa one piece member of requisite spacing thickness and is preferably PTFEto minimize wear and provide lubrication effect. Screw holes 48 areprovided for securement. The surrounding spacing member enables stencilsand substrates of a shorter length with shorter aperture foils 33Mwithout loss of paste.

In a screen printing apparatus, once the apparatus of the invention islocated under the pressure members and one of such has been applied tothe apparatus of the invention, then such together with the whole of thestencil are lowered on to a board/substrate positioned therebeneath,prior to the application of paste and it is in accordance with thepresent invention that a screen printing apparatus may be provided with,or modified so that, a pressure switch, such as a microswitch, detectswhen such lowering takes place and issues a signal to the pneumaticcontrol of the apparatus of the invention to switch over thepressurisation from one cartridge to the other etc. and release pressurefrom the pressurised cartridge.

It is to be appreciated that the present invention enables an existingsqueegee blade operating printing machine to be modified by removal ofthe squeegee blades and the application of two adapter blades withcentral location means and then the simple disposition of the presentapparatus under the pressure arms and blades thereon and with theprovision of a pneumatic control circuit and the mentioned pressureswitch, the adaption can be effected very simply and effective andeconomically. The machine can readily be re-converted to use withexisting squeegees by reversal of the process.

It is desirable to store solder paste at low temperature such as in arefrigerator, and during downtime, after use, for example, the apparatusof the invention may be simply removed from under the adapter's blades12,13 and a sealing retaining strip or other means secured over thelowermost aperture 19 to close such or the aperture may be sealed withself-adhesive tape and then stored in a refrigerator until next requiredfor use.

To give some idea of the volumes of paste media or other fluid involved,for an average stencil for solder paste printing, the operative area mayhave some two thousand apertures through which paste is to be depositedand with an average size of say 1.5 mm by 0.5 mm and a thickness of 0.15mm, the volume of paste to be deposited during each stencillingoperation/stroke of the machine some 225 cubic millimeters wouldactually be required for the stencilling. However, in apparatusaccording to the invention some 1,225 cubic millimeters of paste iscaused to move with each stroke of the machine and thus movement of somefive times the amount of paste actually required for stencilling takesplace and therefor the rheology is improved five-fold.

In FIGS. 19-28 and FIGS. 29-36 the preferred embodiment of the inventionis illustrated and comprises an applicator device 50 made up of a mainpart of a print-head or body 51 formed as an aluminium extrusion andhaving a pressure reduction and mounting means 52 for mounting of aresilient O-ring 53 in a groove 54 in the lower side and for mounting asealing gasket 55 formed of thin flexible and resilient steel sheet/foilin elongate channels or grooves 56 along each side. The pressurereduction and mounting means 52 is secured by two bolts 57 which extendthrough apertures 58 (and through apertures 59 in auxiliary pressurereduction plate 60, when provided, —FIG. 28—having smaller apertures 61aligned with apertures 52 and for use with less viscous fluids).

There is thus provided in the cross-head applicator device 50 a higherfluid pressure chamber or duct 62 on a lower pressure chamber or duct 63each running substantially the length of the device 50.

Two end inlet and cartridge connection means or manifolds 64,65 withsealing gaskets 66 are secured by screws (not shown) in apertures 67,68to each end of body 51 and have passages (not shown) communicating withhigher pressure duct 62 and with a coupling pipe 69 to which fluidreservoirs or cartridges 70,71 may be connected by screwing thereto orby other quick coupling means, if desired. The cartridges 70,71 areknown items and the fluid may be discharged therefrom under pressure bypneumatic action via pipelines coupled at 72 and coupled to controlmeans—see arrow indications—operating in synchronism with the movementsof the screen printing machine of which only the displacing means areillustrated. A piston (not shown) is provided in each cartridge 70,71 todrive fluid from the cartridge when desired. Preferably fluid will bealternately discharged from the cartridges 70,71 during strokes ormovements of the screen printing machine with more fluid beingdischarged during each stroke than is needed to be deposited through thestencil and this is achieved by enabling some fluid to flow back intothe unpressurised cartridge and vice versa. This extra fluid flowimproves the characteristics of the fluid especially when such is solderpaste, Because significant pressure is required for the discharge from acartridge 70,71 and into the other cartridge, and more than is necessaryfor the stencilling operation, a pressure reduction is enabled by theapertures 52′ or 61 when provided.

The bolts 57 which clamp the pressure reduction and mounting means 52 tobody 51 also secure two plastics or metal coupling cylinders 73 to thetop of body 51. In known solder paste screen printing machines as usedin the electronics industry and to which the applicator device 50 of theinvention may be readily connected, a displaceable carriage 74 isreciprocably driven over a metal stencil 75 tensioned between a frame 76and beneath which stencil there is located during each stroke of thecarriage 74 a substrate (not shown) by means of a reciprocably lowercarriage (not shown) and which is to have solder paste applied theretoin accordance with the apertures 77 in the stencil. In the knownmachines, a vertical reciprocating mechanism 78 is provided having twoyokes 79,80 to each of which, hitherto, a so called “squeegee” blade(not shown) was attached via threaded members and nuts in channels81,82. These squeegees during each pass or stroke of the machine arealternately raised or lowered depending as to whether it was to slidealong the stencil surface driving/rolling a bead of solder paste infront of it. The present invention most advantageously enables existingmachines to be readily adapted to use the applicator device of theinvention or any other suitable device with very little modification ofthe existing machine and by simply disconnecting the known squeegeeblades from the channels 81,82 of the carriages 79,80 and replacing suchwith adapter blades 83,84 secured by internally threaded knurled caps 85on threaded rods 86 extending from the top surfaces of adapter blades83,84. The blades 83,84 reduce in section to the lower ends andalternately bear on the top surface 51 of body 51 either side ofcylinders 73 but at all times in sliding abutting relationship—withopposite sides of cylinders retained 73 in small receiving/retainingrecesses (not shown) for parts of cylinders 73 being provided in theopposite faces of the adapter blades 83,84 so as to also locate thedevice 50 against any undesired lateral or axial displacement. Thus thedevice of the invention is readily retained and displaced by beingsecurely located or clamped in between the blades 83,84 which may slidevertically relative to cylinders 73 and the applicator device is thusdriven horizontally in the existing machine drive. It is considered theadapter arrangement also provides an independent inventive aspectaccording to the invention. To accommodate for the alternate lifting offof each blade 83,84, spring means (not shown) may be provided so as toalways maintain pressure on both sides of the applicator device to avoidany undesired pressure reduction or tilting effect on one side.

Returning now to describe more fully a most important inventive aspectof the interface between the applicator device 50 and the stencil 75 andin particular the nature of the sealing means or sealing gasket 55, a“shoe” at spacing member 85 of approx. 3 mm thickness is provided ofPTFE so as to readily slide in the stencil and is backed by a stiffeningor strengthening metal plate 86—especially of importance if the spacingmember 85 extends beyond the end of the body 51. Both shoe member 85 andplate 86 have the same outline and define a central rectangular aperture85′ and 86′ within which gasket 55 lies and are secured via twelveapertures each to threaded apertures 87 in body 51 by screws 88 whoseheads lie in countersunk recesses so as not to extend beneath the member85.

The sealing member or sealing gasket 55 as shown in FIG. 25 is comprisedof a thin flexible and resilient sheet of steel having an elongatecentral aperture 55 a with straight sides and inner edges 55 b androunded ends 55 c and has detents 55 d which act to locate the gasket bystopping against the end of walls 56′ which partly define grooves 56. InFIG. 26 instead of a single aperture as outlet passage as in FIG. 25, ahoneycombe-like mesh 55 e defining a plurality of apertures is shown fordifferent applicators.

Walls 56′ do not extend beneath the lower surface of sliding spacingmember 85. Inclined channels 89 are provided in the lower surface ofmember 85 for disposal of any inadvertent leak of fluid.

The thickness of the spacing member 85 and the shape and size anddisposition of the sealing member 55 and its securement and the size andlocation of the O-ring 53 are selected so that the inner edges 55 b ofthe gasket (which also extend around the rounded ends) are flexed andproject slightly beneath the plane of the spacing member 85 (see FIG.24) when not placed on a support surface, and to an extent such thatwhen placed on a planar support surface, the gasket 55 is forcedupwardly against the O-ring 53 and its own resilience so as to cause asealing action by the flat portion surface against the stencil surface.It will be appreciated that the sealing action is a physical provisionby virtue of the construction etc., and not dependent on the fluidpressure. The O-ring 53 acts against the upper continuous peripheralportion of the sealing gasket to force the lower continuous peripheralportion of the gasket against the stencil surface and, in use, the innerportions of the continuous peripheral portion defining edges 55 b,55 cwill be in a substantially horizontal plane i.e. the plane in which thelower face of sealing member 55 lies.

In FIG. 23 a clear plastics “keeper block” is illustrated which may belocated over the bottom of the device 50 when it is desired to prime orload the head—a closeable air vent V being provided to enable air toescape since the seal is so good. Two further apertures are alsoprovided for securing the block against the shoe and gasket by screwmeans (not shown). The block can be used for storing the applicator whencharged with paste—hole V being closed.

There will now be described modifications wherein blanking-off platesare provided to enable the applicator device to be used on substrates ofless width than the device 50 and also the formation of the sealinggasket or sealing member instead of as a planar member but withpre-formed inclined side walls and part-conical opposite end portionsfor improved sealing effect.

It has been found that the sealing means or sealing gasket havingrounded continuous peripheral portions at opposite ends of an elongateaperture which is planar in its normal unmounted condition, can besubstantially improved if the rounded ends are pre-formed or pre-shapedeach as a part or half-conical surface which results in a very goodsealing effect with the rounded ends of the O-rings and the stencil.

In FIG. 29 the sealing gasket 55 is illustrated in flat form as a“development” and can be manufactured from such flat form and this is astage in the eventual gasket manufacture where the sheet metal is etchedto such shape of FIG. 29 and lies flat with one elongate side beingdivided into two portions 90,91 inclined relative to each other and theother side 92, with the opposite sides of opposite end regions 93,94being half-etched so that they may overlie in abutting interrelationshipso as to have the total thickness of the sheet of the material fromwhich the gasket is made and then may be secured 95 in such manner byspot welding and/or adhesive (and possibly with additional tie platesadded if required) and the resultant of sealing gasket is as illustratedin FIG. 30 wherein prior to this the member is bowed in its free formbut here the outer edges of the long sides have been disposed paralleland in the same plane and the sides will have inclined surfaces (in useconverging inwardly and downwardly) and, whilst it is neither clearlyshown, the opposite curved end portions 96 are part-conically inclinedsurfaces. In the first described arrangement, two joined side portionsmay be provided as a lap joint and bonded by spot welding and/oradhesive together with other means 95 if required. This pre-forming orpre-stressing with inclined sides and part conical ends of the gasketprovides for an exceptional good sealing effect at the ends and in factcontinuously all round.

In the previous description reference has been made to a possibility ofmodifying and shortening the effective application width of theapplicator device by replacing the pressure reduction and mountingmember 52 with a shorter member and shorter O-ring 53 and a shortersealing gasket 55 although a simpler possibility is now proposed inFIGS. 31 to 35 wherein blanking-off parts 97,98,99 may be located atopposite end regions of the lowermost aperture and sealingly heldbetween the O-ring 53 and the continuous portion of the sealing gasket55 and two of such blanking-off ends are shown in FIGS. 31 and 32 beingof different lengths—one of each identical blanks being located atopposite ends and retained in position such as part 98 illustrated atone end in FIG. 34. In FIG. 35, a blanking-off part 97/98 is shown insection having a guide or locating member 102 (of say 0.1 mm) spotwelded thereto (such as via small holes illustrated in FIGS. 31 to 33)which has rounded ends and locates between the inner faces of the wallsdefining the groove 54 and positions the lower edge of part 97/98resting on the O-ring 53 inwardly of and above the lowermost surface ofthe O-ring 53 and above the scraping/wiping inner edge 103 of thesealing gasket 55 such that when gasket 55 is flexed upwardly oncontacting a stencil therebeneath to move into a horizontal orsubstantially horizontal plane, the edges abut and fie in thehalf-etched edges 101 to present a flush surface with the rest at thelower face of part 97/98.

It is also envisaged to provide for the user to select the requisiteblanking-off length of part by providing continuous metal strip 99 withsemi etched/scored lines 100 at say 5 mm spacing so as to enable thelength of the blanking-off sections to be determined by the user bysimply breaking off the appropriate lengths. Around the outermostperipheral edges and the rounded end edges of the blanking-off sheetssuch are half-etched at 101 so as to fit closely between the O-ring andthe continuous peripheral portion without any deformation of the latterand provides a smooth flat or substantially flat flush surface with thecontinuous peripheral portion in use. For example the blanking-off sheetmay be 0.2 mm and half-etched to 0.1 mm to use with a gasket of 0.1 mmso that when the gasket is pressed flat so that its actually a flatsurface results (see drawing).

In previous embodiments it has been suggested that the aperture definedwithin the continuous peripheral portion of the sealing gasket might beof different shape and a plurality of apertures, as desired, by formingthe gasket appropriately. However, as an alternative, it is envisagedthat in a manner similar to location of the blanking-off strips 97,98,there may be located in the elongate aperture, an apertured mesh memberof perhaps double the thickness of the sheet of the sealing gasket andhalf-etched around the periphery to provide a similar flush surface asat the end blanking-off strips 97,98. Thus the two components would formthe lowermost apertures to the device.

In FIGS. 36 and 37 there is illustrated an improved construction whereininstead of the print head body 51 and separate mounting andpressure-reduction means 52 of FIG. 21 etc., the body 103 is integrallyformed as an extrusion with a main flow passage 62′ with converginglower side walls 104 somewhat in the shape of an inverted tear drop andthen the lower reduced pressure flow passage 63′ is machined into theextrusion as shown in broken line 106 in FIG. 36 about a verticalcentral plane indicated by broken line 107. It will be appreciated thatthe more the reduced pressure-flow passage 63′ is machined into the mainflow passage 62′ to form a pressure reduction slot S the greater will bethe width of said slot S and hence the lesser the pressure reduction.The slot S may be of constant width or, if the depth of machining isvaried along the longitudinal axis, the width can be changed. Forexample, there may be a narrower width at opposite ends in the region ofthe paste inlet from the reservoir and such may each enlarge, e.g. byway of a taper or divergence to be widest in the middle of the length soas to optimize the distribution of paste along the length of the reducedpressure flow passage 63′.

In FIG. 36 the sealing gasket 55 and O-ring 53 and groove 54 will be asdescribed before but instead of walls 56′, the gasket 55 will be held byinclined edge walls of a plate member 110 which has a central elongateaperture and angled defining walls 110′ including the inclined wall forreceiving the opposite edges of gasket 53 and will be clamped by plate86 and shoe 85 (not shown) which will be modified in shape as necessary.

FIG. 37 is an end elevation of a modified body 108 extrusion withdifferent shape and does not show the formation of the reduced pressureflow passage 63′ which would cut into passage 62′. The extrusion 108mainly differs by formation of cavities 109 at either side for materialsaving purposes.

It is to be understood that the pressure reduction means, such as 20/24,23/24, 23′/24′, 44,52′/61 and S, act as a flow restriction means totemporarily reduce the pressure in the paste during a printing operationwhen it is flowing out of the bottom of the device and through thestencil. Of course, with the pressure reduction means being in the formof flow restriction apertures or a slot, if no paste is removed,pressure in the main flow passage and the dispensing aperture wouldeventually equalize.

What is claimed is:
 1. An application device for use in a stencilprinting machine, which includes a carriage for executing reciprocablestrokes, to apply a fluid material to a surface of a stencil including aplurality of apertures and through the apertures onto a substratedisposed therebeneath, the device comprising: a main body slideablydisposed along the surface of the stencil and including a main flowpassage, and at least one outlet aperture in a lowermost surface thereofthrough which fluid material is in use delivered, the at least oneoutlet aperture being in fluid communication with the main flow passageand in use in sealing contact with the stencil; at least one fluidmaterial reservoir in fluid communication with the main flow passage;and displacement means operable, during each stroke of the stencilprinting machine, to displace an amount of fluid material from the atleast one fluid material reservoir through the main flow passage whichis greater than that delivered through the at least one outlet aperture.2. The device as claimed in claim 1, further comprising: pressurereduction means disposed upstream of the at least one outlet aperture.3. The device as claimed in claim 2, wherein the pressure reductionmeans is disposed between the main flow passage and the at least oneoutlet aperture.
 4. The device as claimed in claim 2, wherein thepressure reduction means is such as to produce a significant reductionof pressure in the order of a ratio of 6 to
 1. 5. The device as claimedin claim 2, wherein the pressure reduction means comprises a flowrestrictor.
 6. The device as claimed in claim 5, wherein the flowrestrictor comprises a partition including one or more apertures.
 7. Thedevice as claimed in claim 1, wherein the fluid material is a viscousmaterial.
 8. The device as claimed in claim 7, wherein the viscousmaterial comprises a paste.
 9. A screen printing apparatus adapted ormodified to incorporate the device as claimed in claim 1 and havingpneumatic control.
 10. An application device for use in a stencilprinting machine to apply a fluid material through apertures in astencil and onto a substrate disposed beneath the stencil, the devicecomprising: a main body slideably disposed in fluid-retainingrelationship with an upper surface of the stencil, and including a mainflow passage along which fluid material is displaceable, and at leastone outlet aperture in a lowermost surface thereof through which fluidmaterial is in use delivered to the substrate, the at least one outletaperture being in fluid communication with the main flow passage and inuse in sealing contact with the stencil; at least one fluid materialreservoir in fluid communication with the main flow passage; andpressure-exerting means for exerting a pressure to the fluid material atat least one end of the main flow passage and thereby displace an amountof fluid material from the at least one fluid material reservoir throughthe main flow passage which is greater than that delivered through theat least one outlet aperture.
 11. The device as claimed in claim 10,wherein the pressure-exerting means is configured to provide acontinuous flow.
 12. The device as claimed in claim 10, wherein thepressure-exerting means is configured to provide an intermittent flow.13. The device as claimed in claim 10, wherein the pressure-exertingmeans is configured to apply a pressure to one end of the main flowpassage such as to cause fluid material to be displaced in one directiontherethrough on operation of the pressure-exerting means.
 14. The deviceas claimed in claim 13, further comprising: accommodation means foraccommodating fluid material displaced through the main flow passage onapplication of the pressure-exerting means which is additional to thefluid material delivered through the at least one outlet aperture. 15.The device as claimed in claim 10, wherein the pressure-exerting meansis configured to apply a pressure to respective ones of the ends of themain flow passage such as to enable fluid material to be displaced inopposed directions therethrough on operation of the pressure-exertingmeans.
 16. The device as claimed in claim 15, wherein thepressure-exerting means is configured to apply a pressure alternately torespective ones of the ends of the main flow passage such as to enablefluid material to be displaced alternately in opposed directionstherethrough on operation of the pressure-exerting means.
 17. The deviceas claimed in claim 15, wherein the pressure-exerting means comprisesfirst and second reservoirs disposed at opposed ends of the main flowpassage such that fluid material delivered from one of the reservoirs tothe main flow passage and not delivered through the at least one outletopening is received by the other of the reservoirs.
 18. The device asclaimed in claim 16, wherein the pressure-exerting means comprises firstand second reservoirs disposed at opposed ends of the main flow passagesuch that fluid material delivered from one of the reservoirs to themain flow passage and not delivered through the at least one outletopening is received by the other of the reservoirs.
 19. The device asclaimed in claim 18, wherein the reservoirs comprise cartridges aspiston-cylinder arrangements, with the pistons being alternatelydisplaceable during each stroke of the stencil printing machine such asto drive fluid material in opposite directions through the main flowpassage and thereby provide for movement of a bulk of the fluid materialduring printing.
 20. The device as claimed in claim 10, wherein thelowermost surface of the main body is substantially planar and thedevice is such as to enable first and second pressure members of thestencil printing machine to be urgeable against receiving means on anupwardly-facing side of the device, whereby the lowermost surface of themain body is in use urged against the upper surface of the stencil, andthe pressure members alternate in application such as to be on adownstream side of the device with respect to the direction of movementof the device and above a sealing edge of the at least one outletaperture.
 21. The device as claimed in claim 10, wherein the at leastone outlet aperture comprises an elongate slot.
 22. The device asclaimed in claim 10, wherein the at least one outlet aperture ismulti-apertured.
 23. The device as claimed in claim 22, wherein the atleast one outlet aperture is one of a grill or mesh.
 24. The device asclaimed in claim 10, further comprising: a sealing member which definesthe at least one outlet aperture, the sealing member comprising aflexible sheet having a continuous, non-apertured outer region.
 25. Thedevice as claimed in claim 24, wherein the main body includes channelsin which the flexible sheet is retained.
 26. The device as claimed inclaim 24, wherein the main body includes a groove, and the sealingmember further comprises a resilient element disposed in the groove tourge the flexible sheet downwardly when the flexible sheet is displacedupwardly by the action of the stencil.
 27. The device as claimed inclaim 24, wherein the flexible sheet comprises a foil.
 28. The device asclaimed in claim 10, wherein the main flow passage includes a convergingwall portion leading to a slot having a width and shape configured suchas to provide one or both of a desired pressure reduction and fluiddistribution to the at least one outlet aperture.
 29. The device asclaimed in claim 10, wherein the fluid material is a viscous material.30. The device as claimed in claim 29, wherein the viscous materialcomprises a paste.
 31. A screen printing apparatus adapted or modifiedto incorporate the device as claimed in claim 10 and having pneumaticcontrol.